package oj;

import java.util.Scanner;

public class Day6F {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        while (sc.hasNext()){
            int row=sc.nextInt();
            int col=sc.nextInt();
            int[][] arr=new int[1000][1000];
            int count=0;
            for (int i = 0; i < row; i++) {
                for (int j = 0; j < col; j++) {
                    if(arr[i][j]==0){
                        count++;
                        if(i+2<row){
                            arr[i+2][j]=-1;
                        }
                        if(j+2<col){
                            arr[i][j+2]=-1;
                        }
                    }
                }
            }
            System.out.println(count);
        }
    }
}
